As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
An information handling system may include one or more power supply units for providing electrical energy to components of the information handling system. Typically, a power supply unit is configured to operate from an input alternating current (AC) source of electrical energy, which the power supply unit converts to a direct current (DC) output. Thus, typically a power supply unit may include a rectifier and/or power factor correction stage to receive the input AC source and rectify the input AC waveform to charge a bulk capacitor to a desired voltage. A direct-current-to-direct-current (DC-DC) stage may convert the voltage on the bulk capacitor to a DC output voltage which may be used to power components of the information handling system. Other PSUs may be powered from a DC input source (e.g., a 48-volt DC input), and such PSUs may comprise a DC-DC converter for converting voltage to a desired level.
In traditional approaches, a power supply unit may be capable of, immediately after removal of the AC source to the power supply unit, providing electrical energy at its output for a period of time using the stored charge on the bulk capacitor to provide an output direct-current voltage. Such a period of time is limited, of course, as once the alternating current input is not available, the bulk capacitor will discharge and the power supply unit will shut down.
As illustrated in FIG. 1, one portion of this period of time is known as a ride-through time Trt and represents a period of time for which the power supply unit continues to generate a direct current output while waiting for reapplication of the AC source. If the AC source is not reapplied within the ride-through time, the available stored energy on the bulk capacitor may fall below a threshold, and the power supply unit may de-assert a signal (e.g., BULK_OK). The de-assertion of the BULK_OK signal signifies entry into a period known as the hold-up time Tup in which the information handling system may use additional energy remaining stored within the bulk capacitor to power components such that components may complete tasks before the power supply unit is no longer able to provide an adequate direct current output voltage (as indicated by signal DC_OK in FIG. 1 de-asserting). For example, in response to an impending shutdown resulting from loss of alternating current input to a power supply unit, a write-back cache may flush data to a non-volatile memory, and the hold-up time may provide sufficient time for the write-back cache to use available electrical energy from the power supply unit in order to complete the cache flush before the power supply unit ceases generating an output voltage as a result of the withdrawal of the input alternating-current waveform. After the hold-up time has expired, the power supply unit may terminate its DC output in an orderly shutdown procedure. As noted above, in some information handling systems, instead of an AC input source, a DC input source may be used. In such instances, similar hold-up time mechanisms and timings may be provided.
In many information handling system which provide main memory as persistent memory (e.g., non-volatile dual-inline memory modules), the cache or the address range of the persistent memory region cannot be configured as write-back due to the fact that the time required to flush “dirty” cache lines from the cache to memory may be greater than the system hold-up provided. In such cases, the cache or the address range of the persistent memory region may be configured in a lower performance write-through mode. Accordingly, such systems may sacrifice performance as an expense of having persistent memory. For highest performance of persistent memory, is may be desirable to be able to enable write-back caching during system runtime.